From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A950C4338F for ; Mon, 26 Jul 2021 12:48:38 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3519860F46 for ; Mon, 26 Jul 2021 12:48:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 3519860F46 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:40968 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1m8029-00075W-DW for qemu-devel@archiver.kernel.org; Mon, 26 Jul 2021 08:48:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44372) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m7zxf-0000BB-PL for qemu-devel@nongnu.org; Mon, 26 Jul 2021 08:43:59 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:54318) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m7zxd-0007qF-W7 for qemu-devel@nongnu.org; Mon, 26 Jul 2021 08:43:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1627303437; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HCvocV3T6etOq4LJes8MZHjrv/Und+zoNnSoa2MEPk0=; b=hmnctlPb2ASFpu8IxfMKanUn0AVdISf7ex7pUOV/RvwAifUG/JIB+RFW15O221mnoJ7BtQ OH5ornBq72b0NqsQtexgvevyhNqyw4A6zP5NOLNqyXV5yqsLXeYMfCU4k6yWfhM+wkz4jd tUNMMnVHVauSyMnmJEY0lMsjGj3Vdvg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-566-7OTR-TLpP3anLL5jFZTHRQ-1; Mon, 26 Jul 2021 08:43:54 -0400 X-MC-Unique: 7OTR-TLpP3anLL5jFZTHRQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1792487D543; Mon, 26 Jul 2021 12:43:53 +0000 (UTC) Received: from dgilbert-t580.localhost (ovpn-113-117.ams2.redhat.com [10.36.113.117]) by smtp.corp.redhat.com (Postfix) with ESMTP id 94D6160C82; Mon, 26 Jul 2021 12:43:51 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, wei.w.wang@intel.com, peterx@redhat.com Subject: [PULL 2/7] migration: Fix missing join() of rp_thread Date: Mon, 26 Jul 2021 13:43:26 +0100 Message-Id: <20210726124331.124710-3-dgilbert@redhat.com> In-Reply-To: <20210726124331.124710-1-dgilbert@redhat.com> References: <20210726124331.124710-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII" Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.717, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: berrange@redhat.com, leobras@redhat.com, david@redhat.com, quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Peter Xu It's possible that the migration thread skip the join() of the rp_thread in below race and crash on src right at finishing migration: migration_thread rp_thread ---------------- --------- migration_completion() (before rp_thread quits) from_dst_file=NULL [thread got scheduled out] s->rp_state.from_dst_file==NULL (skip join() of rp_thread) migrate_fd_cleanup() qemu_fclose(s->to_dst_file) yank_unregister_instance() assert(yank_find_entry()) <------- crash It could mostly happen with postcopy, but that shouldn't be required, e.g., I think it could also trigger with MIGRATION_CAPABILITY_RETURN_PATH set. It's suspected that above race could be the root cause of a recent (but rare) migration-test break reported by either Dave or PMM: https://lore.kernel.org/qemu-devel/YPamXAHwan%2FPPXLf@work-vm/ The issue is: from_dst_file is reset in the rp_thread, so if the thread reset it to NULL fast enough then the migration thread will assume there's no rp_thread at all. This could potentially cause more severe issue (e.g. crash) after the yank code. Fix it by using a boolean to keep "whether we've created rp_thread". Cc: Dr. David Alan Gilbert Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Peter Xu Message-Id: <20210722175841.938739-2-peterx@redhat.com> Reviewed-by: Lukas Straub Signed-off-by: Dr. David Alan Gilbert --- migration/migration.c | 4 +++- migration/migration.h | 7 +++++++ 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/migration/migration.c b/migration/migration.c index 2d306582eb..21b94f75a3 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -2867,6 +2867,7 @@ static int open_return_path_on_source(MigrationState *ms, qemu_thread_create(&ms->rp_state.rp_thread, "return path", source_return_path_thread, ms, QEMU_THREAD_JOINABLE); + ms->rp_state.rp_thread_created = true; trace_open_return_path_on_source_continue(); @@ -2891,6 +2892,7 @@ static int await_return_path_close_on_source(MigrationState *ms) } trace_await_return_path_close_on_source_joining(); qemu_thread_join(&ms->rp_state.rp_thread); + ms->rp_state.rp_thread_created = false; trace_await_return_path_close_on_source_close(); return ms->rp_state.error; } @@ -3170,7 +3172,7 @@ static void migration_completion(MigrationState *s) * it will wait for the destination to send it's status in * a SHUT command). */ - if (s->rp_state.from_dst_file) { + if (s->rp_state.rp_thread_created) { int rp_error; trace_migration_return_path_end_before(); rp_error = await_return_path_close_on_source(s); diff --git a/migration/migration.h b/migration/migration.h index 2ebb740dfa..c302879fad 100644 --- a/migration/migration.h +++ b/migration/migration.h @@ -195,6 +195,13 @@ struct MigrationState { QEMUFile *from_dst_file; QemuThread rp_thread; bool error; + /* + * We can also check non-zero of rp_thread, but there's no "official" + * way to do this, so this bool makes it slightly more elegant. + * Checking from_dst_file for this is racy because from_dst_file will + * be cleared in the rp_thread! + */ + bool rp_thread_created; QemuSemaphore rp_sem; } rp_state; -- 2.31.1